三峡库区夏季旱涝变化特征及成因

利用1951-2008年三峡库区范围内10个国家基本站的夏季降水资料,通过Z指数分析了三峡库区夏季旱涝的变化特征,确定出6个严重涝年(1954,1956,1980,1982,1983年和1998年)和6个严重旱年(1959,1966,1972,1976,2001年和2006年)。结合NCEP/NCAR的再分析资料以及NOAA的OLR资料,对严重旱涝年份的大气环流形势进行合成分析。结果表明:三峡库区夏季旱涝变化具有较好的一致性,1979年经历了由旱到涝的年代际转变;2001年后,三峡库区进入偏旱阶段。三峡库区夏季严重涝年和旱年环流形势存在显著差异,当100hPa南亚高压异常强大,500hPa高度距平场欧亚高纬度地区从自西向东呈"-+-"距平波列分布,乌拉尔山和鄂霍次克海地区有持续性阻塞高压发展,西太平洋暖池对流偏弱,西太平洋副热带高压位置易偏南,三峡库区以南的西南水汽输送增强,使得三峡库区的水汽辐合增强,这种环流形势配合有利于三峡库区洪涝的发生,严重旱年则相反。

Variation Characteristics and Causes of the Flood and Drought in the Three Gorges Area in Summer

The Three Gorges area is located in the East Asian monsoon region. Under the influence of the monsoon activity, the precipitation of the Three Gorges area mainly concentrates on the period from June to August with relatively high variability, which is prone to the occurrence of the flood and drought disaster. The flood and drought of the Three Gorges area not only has a great impact on the lives of local residents and social activities, but also directly determines the operation and power generation efficiency of the Three Gorges Hydropower complex Project. As a result, the study of the variation characteristics and the formation of the flood and drought of the Three Gorges area is of great significance, providing a scientific decision base to prevent the disaster of flood and drought.
The temporal evolution of the drought and flood of the Three Gorges area in summer and its circulation patterns in the anomalous years are analyzed, obtaining a consistent result. The droughts occur frequently in the Three Gorges area in summer from 1951 to 1978. Following, there is a decadal abrupt change from the droughts to the floods in 1979. Then the floods are popular in the Three Gorges area from 1979 to 2000. Severe droughts take place frequently in the Three Gorges area after 2001. The circulation patterns are obviously different between in severe flood years and in severe drought years of the Three Gorges area. As for the severe flood years of the Three Gorges area, the South Asia High strengthens in 100 hPa, and there is a "－+－" wave train from the west to the east of the Eurasia high latitude area in 500 hPa height anomaly, which reflects that there are continuing block highs in the Okhotsk and Ural regions. Furthermore, the weaker convections over the Western Pacific Warm Pool make the West Pacific Subtropical High to shift southward. In addition, there is strengthening southwest water vapor transport from the Three Gorges area to the Indo China peninsula, which enhances the water vapor convergence in the Three Gorges area. These circulation patterns are advantageous to the genesis of the floods in the Three Gorges area.